The present invention relates to a method for producing AlMn strips or sheets for producing components by soldering.
For example, heat exchangers for motor vehicles are typically produced from aluminum sheets, in that the individually premanufactured components of the heat exchangers, such as plates, pipes, and distributors, are connected to one another by soldering. The stresses which, in practical use, act on components produced in this way installed in automobiles, due to shocks, vibrations of longer duration, the effect of corrosion, and similar things, are significant. This particularly applies to the plates, via which the dissipation of heat occurs.
Defects in these heat exchanger components which occur as a consequence of inadequate properties of the aluminum material may lead to significant damage. In this context, those regions of the components concerned in which changes of the microstructure occur due to the heat arising during soldering have been shown to be particularly problematic in the past.
For the reasons described above, in addition to good suitability for soldering, high strength, particularly a high limit of elasticity Rp0.2, and toughness even after soldering are required of aluminum sheets of the type under discussion. The aluminum sheets concerned must simultaneously have good deformability and a high resistance to corrosion.
A material for producing plates for heat exchangers is known from WO 97/18946 which contains (in weight-percent) 0.2-0.5% Fe, 0.7-1.2% Si, 1.2-1.6% Mn, xe2x89xa60.3% Mg, xe2x89xa60.05% Cu, xe2x89xa60.2% Zn, xe2x89xa60.1% Ti, and unavoidable companion elements whose individual amounts are at most 0.05% and whose sum is at most 0.15%, as well as aluminum as the remainder. Ingots are cast from this material as a precursor material, which are subsequently preheated to an initial rolling temperature of at least 520xc2x0 C. and hot rolled. The cold rolling to the final thickness which follows this is performed in at least two steps, with an intermediate annealing having to be performed for two hours at an annealing temperature lying between 360xc2x0 C. and 400xc2x0 C. between the cold rolling steps.
It has been shown in the practical testing of the material produced according to the known method that the material properties of the aluminum sheets produced according to the related art are insufficient for specific applications. This particularly applies for the strength and corrosion resistance still existing after soldering in the region of the soldering joints. In addition, it has been shown in, for example, the production of heat exchangers that the possibilities for the combination of components produced from the material known from WO 97/18946 with heat exchanger components produced from another light metal material are restricted due to the difference of the corrosion potentials, which is too low.
The object of the present invention is, based on the related art described above, to indicate a method by which aluminum sheets may be produced in a cost-effective way, which, even after soldering, reliably have a high strength, particularly a high limit of elasticity, as well as outstanding corrosion resistance. This object is achieved by a method for producing components by soldering.